Method and device for operating an internal combustion engine

ABSTRACT

The disclosure relates to a method for operating an internal combustion engine having a plurality of cylinders, the method comprising, during one working cycle, distributing fuel for each cylinder of the plurality of cylinders among a plurality of injection processes according to settable split factors which respectively define a setpoint fuel mass and/or injection duration and time setting of each respective injection process for the plurality of individual injection processes, wherein random variation is carried out for at least one injection process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Patent Application No.102012209785.6, filed on Jun. 12, 2012, the entire contents of which arehereby incorporated by reference for all purposes.

FIELD

The disclosure relates to a method and to a device for operating aninternal combustion engine. In particular, the disclosure relates to amethod and to a device for operating an internal combustion engine bymeans of which instability in the running of the engine which occursduring operation of the engine and is due to the generation of pressurewaves can be avoided or at least reduced.

BACKGROUND AND SUMMARY

The operation of an internal combustion engine with multiple injections(also referred to as “split injection”) is used, inter alia, forreducing particle emissions. In this context, the conventional injectionof an individual fuel injection during the working cycle is replaced bythe injection of a plurality of chronologically distributed fuelinjections, wherein comparatively less fuel is used for each individualinjection process than in the case of an individual injection.

However, a problem which occurs in practice in the case of multipleinjections is that pressure waves which occur in the fuel line ofsystems with high fuel pressure during operation in a mode with multipleinjections can cause the internal combustion engine to operate in anunstable fashion.

This instability is caused by undesired deviation in the actualinjection quantity brought about by pressure pulsations in the commonfuel line. Depending on the distribution and chronological arrangementof the multiple injections at all the cylinders, these high pressurepulsations can occur due to unfavorable superimposition of theexcitation as a result of the respective extraction of fuel.

The inventors herein have recognized the above issues and provide amethod to at least partly address them. In one embodiment, a method foroperating an internal combustion engine having a plurality of cylinderscomprises, during one working cycle, distributing fuel for each cylinderof the plurality of cylinders among a plurality of injection processesaccording to settable split factors which respectively define a setpointfuel mass and/or injection duration and time setting of each respectiveinjection process for the plurality of individual injection processes,wherein random variation is carried out for at least one injectionprocess.

Thus, the method according to the disclosure for operating an internalcombustion engine comprising a plurality of cylinders, during oneworking cycle, the fuel injection for each of the cylinders isdistributed among a plurality of injection processes according tosettable split factors which respectively define the setpoint fuel massand/or the injection duration and the time setting of the respectiveinjection process for the individual injection processes, wherein randomvariation is carried out for at least one injection process.

The present disclosure is based, in particular, on the concept ofperforming random variation of the split factors for individualinjection processes within a range defined by a tolerance value duringan operating mode of the internal combustion engine with multipleinjections. By means of such a device or by increasing the splitting orapportioning of the fuel injection for the individual injectionprocesses it is possible as a result to reduce the pressure waves withinthe fuel line. In this context, a reduction in pressure waves within thefuel line can already be achieved by marginal change in the splitfactors for each injection process and each cylinder.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of a vehicle system including anengine.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof the engine of FIG. 1.

FIG. 3 shows a block diagram which shows an overview of the componentsused in a method according to the disclosure.

FIG. 4 shows a block diagram explaining in more detail a split unitwhich is present in the arrangement in FIG. 3.

FIG. 5 shows a block diagram explaining in more detail a furtherfunctional block which is present in the split unit in FIG. 4.

FIGS. 6-8 are flow charts illustrating methods for randomly varyingsplit injection parameters according to embodiments of the disclosure.

FIG. 9 is a diagram illustrating an example sequence of fuel injectionevents for a plurality of cylinders.

DETAILED DESCRIPTION

Engines may be configured to operate under a split injection mode,wherein more than fuel injection is performed to a given cylinder duringa cylinder cycle. Depending on the frequency of the injections, pressurewaves may build in the fuel system, leading to degradation of the systemcomponents. To disrupt and/or prevent such waves, various parameters ofthe fuel injections may be randomly adjusted. For example, the fuel massof a first injection event of a plurality of injection events of acylinder may be randomly adjusted away from the setpoint fuel massdetermined based on operating conditions. The adjusted fuel mass may becompensated by adjusting a later fuel injection event (performed to thesame cylinder during the same cylinder cycle).

According to the disclosure, the random variation can occur in the timesetting for at least one injection process. According to a furtherembodiment, the random variation is carried out by means of the timesetting of at least one injection at one cylinder in such a way that theexcitation of the pressure pulsations is detuned.

According to one embodiment, the random variation of the setpoint fuelmass and/or of the injection duration therefore takes place for at leasttwo injection processes in such a way that pressure waves which occurare reduced in comparison with an analogous operation without the randomvariation.

According to a further embodiment, the random variation takes place bothin the time setting for at least one injection process and in thesetpoint fuel mass and/or injection duration for at least two injectionprocesses.

According to a further embodiment, the random variation of the setpointfuel mass takes place for at least two injection processes in apredefined tolerance range. According to a further embodiment, therandom variation of the setpoint fuel mass takes place for at least twoinjection processes in such a way that pressure waves which occur arereduced in comparison with an analogous operation without the randomvariation.

According to one embodiment, the random variation of the setpoint fuelmass takes place for each of the cylinders in such a way that the sum ofthe setpoint fuel masses which are to be injected in all the injectionprocesses remains unchanged for the respective cylinder.

According to one embodiment, the method also has a fault diagnosis stepin which a fault message is generated as a function of the value of thesum of the split factors. This can take place, in particular, when thesum of the split ratios for a respective combustion cycle is greaterthan one (and/or is greater than 100%).

The disclosure also relates to a device for operating an internalcombustion engine comprising a plurality of cylinders and which isconfigured to carry out a method having the features described above.

FIG. 1 shows a schematic depiction of a vehicle system 6 including anengine system 8. The engine system 8 may include an engine 10 having aplurality of cylinders 30. Engine 10 includes an engine intake 23 and anengine exhaust 25. Engine intake 23 includes a throttle 62 fluidlycoupled to the engine intake manifold 44 via an intake passage 42. Theengine exhaust 25 includes an exhaust manifold 48 eventually leading toan exhaust passage 35 that routes exhaust gas to the atmosphere.Throttle 62 may be located in intake passage 42 downstream of a boostingdevice, such as turbocharger 50, or a supercharger, and upstream of anafter-cooler (not shown). As such, the after-cooler may be configured toreduce the temperature of the intake air compressed by the boostingdevice. Turbocharger 50 may include a compressor 52, arranged betweenintake passage 42 and intake manifold 44. Compressor 52 may be at leastpartially powered by exhaust turbine 54, arranged between exhaustmanifold 48 and exhaust passage 35, via turbine shaft 56.

Engine exhaust 25 may include one or more emission control devices 70,which may be mounted in a close-coupled position in the exhaust. One ormore emission control devices may include a three-way catalyst, lean NOxfilter, SCR catalyst, PM filter, etc.

Engine system 8 may further include one (as depicted) or more knocksensors 90 distributed along engine block 11. When included, theplurality of knock sensors may be distributed symmetrically orasymmetrically along the engine block. Knock sensor 90 may be anaccelerometer, or an ionization sensor.

The vehicle system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 (located in exhaust manifold 48), knock sensor(s) 90,temperature sensor 127, and pressure sensor 129 (located downstream ofemission control device 70). Other sensors such as pressure,temperature, air/fuel ratio, and composition sensors may be coupled tovarious locations in the vehicle system 6, as discussed in more detailherein. As another example, the actuators may include fuel injectors 66,and throttle 62. The control system 14 may include a controller 12. Thecontroller may receive input data from the various sensors, process theinput data, and trigger the actuators in response to the processed inputdata based on instruction or code programmed therein corresponding toone or more routines. Example control routines are described herein withreference to FIGS. 6-8.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10 (of FIG. 1). Engine 10 may receivecontrol parameters from a control system including controller 12 andinput from a vehicle operator 130 via an input device 132. In thisexample, input device 132 includes an accelerator pedal and a pedalposition sensor 134 for generating a proportional pedal position signalPP. Cylinder (herein also “combustion chamber”) 30 of engine 10 mayinclude combustion chamber walls 136 with piston 138 positioned therein.Piston 138 may be coupled to crankshaft 140 so that reciprocating motionof the piston is translated into rotational motion of the crankshaft.Crankshaft 140 may be coupled to at least one drive wheel of thepassenger vehicle via a transmission system. Further, a starter motormay be coupled to crankshaft 140 via a flywheel to enable a startingoperation of engine 10.

Cylinder 30 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 30. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 2 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 2, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 30 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 30. In some embodiments, eachcylinder of engine 10, including cylinder 30, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 30 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 30 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 30 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 30 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 30 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 30. While FIG. 2shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing.

Fuel may be delivered to fuel injector 166 from a high pressure fuelsystem 80 including fuel tanks, fuel pumps, and a fuel rail. Forexample, fuel tank 19 may store liquid fuel such as gasoline, fuel witha range of alcohol concentrations, various gasoline-ethanol fuel blends(e.g., E10, E85), and combinations thereof. As shown, fuel tank 19 maybe coupled to a fuel pump 21 for pressurizing fuel delivered to fuelrail 51. A fuel rail pressure sensor 102 in fuel rail 51 may beconfigured to sense the current fuel rail pressure and provide thesensed value to controller 12 of control system 14. In some examples,pump 21 may be controlled based on the fuel rail pressure sensed bysensor 102, and/or based on other parameter values. Fuel tank 19 may berefilled with liquid fuel via fueling port 83. Fuel may be deliveredfrom fuel tank 19 to the injectors of engine 10, such as exampleinjector 166, via fuel rail 51. While only a single injector coupledwith the fuel rail is depicted, it will be appreciated that additionalinjectors are provided for each cylinder.

Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tankmay have a pressure transducer providing a signal to controller 12. Itwill be appreciated that, in an alternate embodiment, injector 166 maybe a port injector providing fuel into the intake port upstream ofcylinder 30.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; absolute manifold pressure signal (MAP) from sensor124, cylinder AFR from EGO sensor 128, and abnormal combustion from aknock sensor and a crankshaft acceleration sensor. Engine speed signal,RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

FIG. 3 first shows an overview of the components used in a methodaccording to the disclosure for operating an internal combustion enginein the multiple injection mode. In one example, the components depictedin FIG. 3 may be included as part of controller 12 described above.

According to the block diagram in FIG. 3, a split unit 107 serves tocalculate the fuel mass to be injected from the required fuel mass foreach injection process, which fuel mass to be injected is defined by atorque model. The calculated fuel mass is identical for the respectiveinjection processes for all the cylinders. In this context, it ispossible to set different split ratios for each state of the internalcombustion engine.

An injection duration unit 121 serves to calculate the injectionduration for each injection process. This calculation includes pressuredifferences over the respective injection process, which includescalculation of the internal pressure of the cylinder as a function ofthe valve timing and the dynamic fuel flow for each injection nozzle.

A time setting unit 131 serves to set the time of the individualinjection processes, wherein this time setting for each injectionprocess is defined by the start of injection (SOI) and the end ofinjection (EOI). Within the time setting unit 131 the start of injection(SOI) can be set manually for each engine state. Depending on the stateof the internal combustion engine, the injection system can permit upto, for example, five injection processes per cylinder and engine cycle.In this context, the start of injection is typically set for the first,the second, the third and the fourth injection process, whereas for thefifth injection process the end of injection (EOI) is set. In the caseof stratified combustion or stratified loading operation, the fifthinjection process can also be coupled with the injection setting.

According to FIG. 4, the split unit 107 in the exemplary embodiment isdivided into three functional blocks 111, 109 and 113. A firstfunctional block 111 permits a ratio to be set which defines thesplitting for each engine cycle and for all the cylinders. The ratio canbe predefined for each engine state or set manually. Furthermore,according to FIG. 4 simple multiplication of the individual split ratiosby the fuel mass calculated on the basis of the torque model takesplace.

For each of the five injection processes, according to FIG. 4 a splitratio (or a split factor) can be set in the function block 111, whichsplit ratio (or split factor) defines the setpoint fuel mass (mf_inj),the injection duration (ti_dinj_dur) and the time setting(a_inj_soi/a_inj_eoi) determined by the start of injection and the endof injection. In this context, it is possible to set dynamically foreach injection nozzle, in a different way, the Q parameter which ispredefined conventionally by the supplier for the injection nozzle.

According to FIG. 4, the setpoint fuel masses (mf_inj_(—)1 tomf_inj_(—)5) are fed to a second function block 109. This secondfunction block 109 according to FIG. 4 serves, as is explained below, toreduce the generation of pressure waves during operation of the internalcombustion engine with multiple injections.

A detailed diagram for explaining this second function block 109 isillustrated in FIG. 54. If the function block 109 is activated, in theexemplary embodiment random variation of the fuel mass takes place forthe first injection process and for the second injection process,whereas the third injection process remains unchanged. This variationtakes place in a random block which is provided for this purpose, in aregion which is defined by a predefined tolerance value. By means ofsuch a reduction or increase in the splitting or apportioning of thefuel injection for the individual injection processes it is possible asa result to reduce the pressure waves within the fuel line.

In this context, in order to maintain the engine load, it is necessaryfor the resulting sum of the setpoint fuel masses to be injected toremain unchanged. If, for example, in the above example the fuel masswhich is used for the first injection process is reduced by threepercent (%), the fuel mass which is used for the second injectionprocess must be increased by a factor which results in the same setpointfuel mass.

Furthermore, according to FIG. 5, the five injection ratios for aninjection process are combined in one vector “rat_inj_spli”. As is alsoapparent from FIG. 5, in a third function block 113 it is checkedwhether the sum of the split ratios for a respective injection cycle isgreater than one (corresponding to a value above 100%), in which case afault message is generated.

Turning now to FIG. 6, a method 600 for injecting fuel to an engine isdepicted. Method 600 may be carried out by an engine controller, such ascontroller 12 of FIGS. 1 and 2, according to instructions storedthereon. Method 600 sets the parameters of fuel injection for eachcombustion event of each cylinder of an engine based on operatingconditions, and then if indicated, randomly varies at least one of theinjection parameters to prevent or disrupt pressure pulsations withinthe fuel rail or other fuel system components.

At 602, engine operating parameters are determined. The operatingparameters may be determined from signals received from various enginesensors. For example, engine speed, engine load, engine temperature,duration since an engine start, fuel rail pressure, exhaustaftertreatment regeneration state, and other parameters may be measured,estimated, or inferred.

At 604, fuel injection parameters are set based on the previouslydetermined operating conditions. The fuel injection parameters include asplit ratio, which includes the number of injections performed at eachcylinder per combustion cycle and the fuel mass of each split injection,injection timing (start and/or end of injection), and injectionduration. The injection parameters may be optimized for differentoperating parameters. For example, during an engine start sequence,fewer injection events may be performed than during engine runningconditions. Further, a purge or regeneration of an exhaustaftertreatment device (such as a lean NOx trap or particulate filter)may rely on increased exhaust temperature; the fuel injection parametersmay be adjusted during the purge to increase the exhaust temperature.

At 606, method 600 includes split injecting fuel to a cylinder.Injecting fuel to a cylinder includes, at 608, injecting a total fuelmass based on desired air-fuel ratio (AFR). That is, the total amount offuel injected to one cylinder during one cylinder cycle may be selectedto maintain air-fuel ratio at a desired ratio (such as stoichiometry)and deliver a requested amount of torque. Further, as indicated at 610,this total fuel mass is distributed among the split injections accordingto the split ratio set at 604.

Upon commencement of fuel injection, fuel injection pressure ismonitored at 612. The monitoring of fuel injection pressure may includemonitoring fuel rail pressure, the pressure in one or more linesdelivering fuel from the rail to the injectors, the pressure of theinjectors themselves, and/or other suitable pressures. At 614, method600 determines if a repetitive pressure fluctuation is detected. Therepetitive pressure fluctuation may include a pressure wave propagatedin the fuel rail, fuel delivery lines, or other fuel system components.The repetitive pressure fluctuation may be detected based on themonitored fuel injection pressure.

In one example, pressure waves with amplitudes below a threshold may notbe detected as a repetitive pressure fluctuation. The thresholdamplitude of the pressure wave may be an amplitude above whichdegradation to an engine component may occur, and/or it may be anamplitude above which vibrations may be noticeable to a vehicleoperator. The pressure fluctuation may be repetitive, that is occurringat least more than one time in a give time period.

If a repetitive pressure fluctuation is not detected, method 600proceeds to 616 to maintain the fuel injection parameters determined at604, and method 600 returns. If a repetitive pressure fluctuation isdetected, method 600 proceeds to 618 to randomly vary one or more splitinjection parameters to disrupt the pressure fluctuation. This mayinclude randomly adjusting the split ratio and/or duration, as indicatedat 620 and explained in more detail below with regards to FIG. 7.Further, randomly varying one or more split injection parameters mayinclude randomly adjusting injection timing, as indicated at 622 andexplained in more detail below with regards to FIG. 8. The randomadjustment to the fuel injection parameter or parameters may beperformed on the current combustion cycle, or it may be performed on asubsequent combustion cycle. Further, this random adjustment may beapplied to the fuel injection of a single cylinder of a multi-cylinderengine, while maintaining the initial injection parameters of theremaining cylinders, or it may be applied to the fuel injection eventsof more than one cylinder of the engine.

The random adjustment to the fuel injection parameters may alter themass of fuel delivered during two or more split injections. To ensurethat the total mass of fuel is delivered to the cylinder, the fuel massof each split injection may be summed and compared to the target totalfuel mass, set based on desired air-fuel ratio. At 624, it is determinedif 100% of the total fuel mass is delivered. If no, that is, if more orless fuel than desired is actually delivered, method 600 proceeds to 624to set an error flag, and take default action. For example, the randomadjustment may be ceased, additional fuel may be injected in asubsequent combustion event, etc.

If 100% of the total fuel mass is delivered, method 600 optionallyproceeds to 626 to repeat the random variation for subsequent combustioncycles, and then method 600 returns.

Turning now to FIG. 7, a method 700 for randomly varying a split ratioof a cylinder fuel injection event is illustrated. Method 700 may beperformed by a controller, during the execution of method 600 explainedabove, responsive to an indication to randomly vary the mass and/orduration of a given split fuel injection. Method 700 includes, at 702,determining an initial fuel mass of a first split injection. The initialfuel mass may be determined based on a total fuel mass to be deliveredto the cylinder and a fraction of that fuel mass that is to be deliveredby the first injection, otherwise referred to as the split ratio. Forexample, if three fuel injections of equal mass are to be performed on asingle cylinder during a given combustion cycle, the initial fuel massof the first split injection may be ⅓ of the total fuel mass.

At 704, a tolerance function is applied to maintain the first fuel massin a threshold range. For example, the tolerance function may limit therandom variation, described below, to adjusting the first fuel mass byless than a threshold amount, such as 10%. Because the fuel injectionparameters are set based on operating conditions (to deliver the fuel inamounts and timings optimized for maximizing power, minimizingparticulates, or other desired outcomes), major adjustments to theamount of fuel delivered by a split injection could result in diminishedtorque, excess particulates, or other undesired conditions. Thus, thetolerance function may maintain the variation to the injectionparameters within a range that allows disruption of the pressure waveswithout perturbations to fuel efficiency, emissions, or otherparameters.

The range of variation imposed by the tolerance function may be asuitable range. For example, it may be a fixed range, such as avariation of less than 10%. In other examples, the tolerance may dependon the initial injection parameters. As an example, if the initial fuelmass that the first split injection is intended to deliver is relativelysmall, the tolerance may only allow a 2% decrease in the fuel mass, toprevent metering errors that may occur when delivering small amounts offuel, while allowing a larger increase in the fuel mass, such as 5%.

At 706, a random variation function is applied to the initial fuel massof the first split injection. The random variation function may be arandom number generator, bounded by the tolerance described above, suchas a true random number generator or a pseudo-random number generator.In one example, the fuel mass and/or duration of fuel injection may beadjusted by a percentile amount specified by the random variationfunction. Further, in some embodiments, other filters or functions maybe applied to generate the variation applied to the fuel mass, such as aGaussian function. Further still, additional functions may be applied tothe random number generated by the random number generator, to ensurethe number is different from the last random number generated, forexample.

At 708, the fuel mass and/or duration of the first split injection maybe adjusted based on the random variation applied at 706. For example,the fuel mass of the first split injection may be increased by 5%. Todeliver the adjusted fuel mass, the injection duration may also beadjusted. For example, at a steady fuel injection pressure, in order toincrease the fuel mass of the first split injection by 5%, the durationthat the fuel injector is open may be increased to deliver the extrafuel. At 710, the fuel mass and/or injection duration of the secondsplit injection may be adjusted by a corresponding amount. To maintain adesired or commanded total fuel injection mass for the whole cylindercycle, the second split injection may be adjusted to compensate for thechange to the first split injection. For example, if the fuel mass ofthe first injection is increased by 5%, the fuel mass of the secondsplit injection may be decreased by 5%. In this way, the randomadjustment to the first injection may be compensated by an adjustment tothe second injection in order to deliver the same amount of fuel to thecylinder as would be delivered without the random variation. Thecompensation is typically performed on one other split injection of thecylinder cycle, and thus if a third split injection is performed, itsmass and duration are maintained and not adjusted, as indicated at 712.

FIG. 8 illustrates a method 800 for randomly adjusting injection timingof a split injection. Similar to method 700, method 800 may be performedby a controller, during the execution of method 600 explained above,responsive to an indication to randomly vary the injection timing of agiven split fuel injection.

At 802, method 800 includes determining an initial timing of a firstsplit fuel injection. The timing of the injection may include a start ofinjection, or an end of injection. The injection timing of the splitinjection may be determined based on operating parameters, as explainedabove. At 804, a tolerance is applied to maintain the injection timingwithin a threshold range, similar to the tolerance applied at 704 above.At 806, a random variation function is applied to randomly vary thetiming of the split injection. The random variation may similar to therandom variation performed at 706 of method 700. At 808, the timing ofthe first split injection is adjusted based on the random variationdetermined at 806.

While the methods described above randomly adjust fuel mass or injectiontiming of a split injection, in some embodiments both fuel mass andinjection timing may be adjusted. Further, in some embodiments the fuelmass of a first split injection may be adjusted, and the fuel mass andinjection timing of a second split injection may also be adjusted.Further, the above-described methods randomly vary the fuel injectionparameters responsive to an indication that a pressure wave ispropagating the fuel system. However, in some embodiments, the randomvariation may be carried out proactively before a pressure wave hasbuilt, in order to prevent the build-up of the pressure wave. In suchembodiments, the random variation may be performed automatically at eachcylinder cycle or performed automatically on selected cylinder cycles.

Thus, the methods described provide for a method, comprising splitinjecting fuel in two or more injections into a cylinder during a singlecombustion cycle; and randomly varying at least one of the two or moreinjections. The randomly varying may include randomly varying one ormore of a fuel injection mass, injection timing, and injection duration.In one example, the randomly varying includes randomly varying a fuelinjection mass of a first injection of the two or more injections, andthe method may further comprise adjusting a fuel injection mass of asecond injection of the two or more injections based on, and tocompensate for, the random variation of the first injection, where adesired total amount of injected fuel is maintained for the two or moreinjections even with the random variation. In another example, therandomly varying includes randomly varying an injection timing of one ofthe two or more injections.

In an embodiment, a method comprises split injecting fuel including atleast a first fuel mass and a second fuel mass to a cylinder during afirst cylinder cycle; and randomly varying a split ratio of the firstfuel mass relative to the second fuel mass for each of a plurality ofsubsequent cylinder cycles. The method includes randomly adjusting thefirst fuel mass and adjusting the second fuel mass to compensate for theadjustment to the first fuel mass. Adjusting the first fuel masscomprises adjusting the first fuel mass by less than a threshold amountfrom an initial setpoint fuel mass. The initial setpoint fuel mass maybe set based on engine operating conditions. In embodiments, the methodmay further comprise injecting a third fuel mass during the firstcylinder cycle, wherein the third fuel mass is maintained over eachsubsequent engine cycle. A total mass of fuel injected to the cylindermay remain constant over each subsequent cylinder cycle.

As used in the disclosure, cylinder cycle or combustion cycle may referto, in a four stroke engine, a complete cycle of intake, compression,expansion, and exhaust strokes of a given cylinder. Each cylinder mayundergo a combustion or cylinder cycle in a complete engine cycle.Additionally, while the methods described above randomly adjust fuelmass, duration, and/or timing of a first injection, it is to beunderstood the random adjustment to an injection parameter may beapplied to a suitable injection of the two or more injections performedin a cylinder cycle. For example, if a split injection includes fiveinjection events, the first, second, third, fourth, or fifth injectionmay be randomly varied. Further, if an injection event is randomlyvaried such that its fuel mass is changed, a later fuel injection may beadjusted to compensate for the random variation. Thus, if a firstinjection is randomly varied, a second, third, fourth, or fifthinjection may be adjusted to compensate for the variation. In someembodiments, to compensate for the variation of a first injection, botha second and a third injection may be adjusted. Other injectionadjustments are possible, as discussed in more detail below.

Referring now to FIG. 9, an example split fuel injection sequence isshown. The sequence of FIG. 9 may be provided by the system of FIGS. 1and 2 executing the method of FIG. 6. Cylinder timing for an engineincluding cylinders 1, 2, 3, and 4 is shown. Note that actual fuelinjection times may differ from the timings shown in FIG. 9 since FIG. 9is intended to illustrate the method described herein rather than showparticular fuel injection timings.

The first, third, fifth, and seventh plots from the top of FIG. 9represent cylinder strokes for cylinders number one, three, four, andtwo of a four cylinder engine. Intake strokes are abbreviated INT whilecompression strokes are abbreviated as COMP. Expansion strokes areabbreviated as EXP while exhaust strokes are abbreviated as EXH.

The second, fourth, sixth, and eighth plots from the top of FIG. 9represent fuel injection events for cylinders number one, three, four,and two of the engine. As illustrated in FIG. 9, three injection events(or split injections) occur for each cylinder during each combustioncycle. The first split injection, second split injection, and thirdsplit injection for a first cylinder cycle of cylinder number one areindicated as 902 a, 904 a, and 906 a, respectively. The first splitinjection, second split injection, and third split injection for a firstcylinder cycle of cylinder number three are indicated as 908 a, 910 a,and 912 a, respectively. The first split injection, second splitinjection, and third split injection for a first cylinder cycle ofcylinder number four are indicated as 914 a, 916 a, and 918 a,respectively. The first split injection, second split injection, andthird split injection for a first cylinder cycle of cylinder number twoare indicated as 920 a, 922 a, and 924 a, respectively.

Likewise, the first split injection, second split injection, and thirdsplit injection for a second cylinder cycle of cylinder number one areindicated as 902 b, 904 b, and 906 b, respectively. The first splitinjection, second split injection, and third split injection for a firstcylinder cycle of cylinder number three are indicated as 908 b, 910 b,and 912 b, respectively. The first split injection, second splitinjection, and third split injection for a first cylinder cycle ofcylinder number four are indicated as 914 b, 916 b, and 918 b,respectively. The first split injection, second split injection, andthird split injection for a first cylinder cycle of cylinder number twoare indicated as 920 b, 922 b, and 924 b, respectively.

The number of split injections, as well as the injection timing, fuelmass, and duration for each split injection may be determined based onoperating conditions, as explained above. In the illustrated example,the engine may be operating at idle with stratified combustion, and assuch, for each combustion event at a given cylinder, three splitinjections are performed, with the third split injection timingcorresponding with ignition timing.

During the injections for the first cylinder cycle of cylinder one, eachinjection event 902 a, 904 a, and 906 a delivers an equal fuel mass.However, at the second cylinder cycle, a random variation has beenapplied to the fuel mass of the first injection 902 b, resulting in adecrease of the fuel mass. The second injection 904 b is increased by acorresponding amount. The third injection 906 b delivers the same massof fuel as the third injection 906 a of the first cylinder cycle.

For cylinder three, the random variation has been applied to the firstinjection 908 a of the first cylinder cycle, increasing the fuel mass.The second injection 910 a is decreased by a corresponding amount, andthe third injection 912 a does not change from the initial setpoint fuelmass. For the second cylinder cycle, the first injection 908 b isincreased due to the random variation and the second injection 910 b isdecreased.

For cylinder four, the fuel mass of the first injection 914 a, secondinjection 916 a, and third injection 918 a of the first cylinder cycleare equal to the initial setpoint fuel mass. However, the injectiontiming of the first injection 914 a has been retarded. For the secondcylinder cycle, the timing of the second injection 916 b has beenadvanced.

For cylinder two, the fuel mass of the first injection 920 a of thefirst cylinder cycle has been increased and the fuel mass of the secondinjection 922 a has been decreased. Also, the injection timing of thesecond injection 922 a has been retarded. For the second cylinder cycle,the fuel mass of the first injection 920 b has been decreased, the fuelmass of the second injection 922 b has been increased, and the injectiontiming of the second injection 922 b has been advanced.

Thus, the sequence illustrated in FIG. 9 includes random variation tofuel mass alone in some examples, random variation to injection timingalone in other examples, and random variation to both fuel mass andinjection timing in other examples. Whether random adjustment to theinjection parameters is performed only on one parameter or multipleparameters may depend on the amplitude of the pressure wave, toleranceof the random variation of each injection parameter (for example, if thetolerance for adjusting the fuel mass is very narrow, the injectiontiming may also be adjusted), and other parameters.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for operating an internal combustion engine having aplurality of cylinders, the method comprising, during one working cycle,distributing fuel for each cylinder of the plurality of cylinders amonga plurality of injection processes according to settable split factorswhich respectively define a setpoint fuel mass and/or injection durationand time setting of each respective injection process for the pluralityof individual injection processes, wherein random variation is carriedout for at least one injection process.
 2. The method as claimed inclaim 1, wherein the random variation occurs in the time setting for atleast one injection process.
 3. The method as claimed in claim 2,wherein the random variation is carried out by the time setting of atleast one injection at one cylinder to detune excitation of pressurepulsations.
 4. The method as claimed in claim 1, wherein the randomvariation takes place in the setpoint fuel mass and/or in the injectionduration for at least two injection processes.
 5. The method as claimedin claim 1, wherein the random variation takes place both in the timesetting for at least one injection process and in the setpoint fuel massand/or injection duration for at least two injection processes.
 6. Themethod as claimed in claim 5, wherein the random variation of thesetpoint fuel mass takes place for at least two injection processes in apredefined tolerance range.
 7. The method as claimed in claim 1, whereinthe random variation of the setpoint fuel mass takes place for at leasttwo injection processes to reduce pressure waves in comparison with ananalogous operation without the random variation.
 8. The method asclaimed in claim 1, wherein the random variation of the setpoint fuelmass takes place for each of the cylinders in such a way that the sum ofthe setpoint fuel masses which are to be injected in all the injectionprocesses remains unchanged for the respective cylinder.
 9. The methodas claimed in claim 1, wherein said method also includes generating afault message as a function of a value of a sum of the split factors.10. A device for operating an internal combustion engine comprising aplurality of cylinders, wherein said device is configured to carry out amethod as claimed in claim
 1. 11. A method, comprising: split injectingfuel in two or more injections into a cylinder during a singlecombustion cycle; and randomly varying at least one of the two or moreinjections.
 12. The method of claim 11, wherein the randomly varyingincludes randomly varying one or more of a fuel injection mass,injection timing, and injection duration.
 13. The method of claim 12,wherein the randomly varying includes randomly varying a fuel injectionmass of a first injection of the two or more injections, and furthercomprising adjusting a fuel injection mass of a second injection of thetwo or more injections based on, and to compensate for, the randomvariation of the first injection, where a desired total amount ofinjected fuel is maintained for the two or more injections even with therandom variation.
 14. The method of claim 12, wherein the randomlyvarying includes randomly varying an injection timing of one of the twoor more injections.
 15. A method, comprising: split injecting fuel in atleast a first fuel mass and a second fuel mass to a cylinder during afirst cylinder cycle; and randomly varying a split ratio of the firstfuel mass relative to the second fuel mass for each of a plurality ofsubsequent cylinder cycles.
 16. The method of claim 15, wherein randomlyvarying the split ratio comprises randomly adjusting the first fuel massand adjusting the second fuel mass to compensate for the adjustment tothe first fuel mass.
 17. The method of claim 16, wherein adjusting thefirst fuel mass comprises adjusting the first fuel mass by less than athreshold amount from an initial setpoint fuel mass.
 18. The method ofclaim 16, further comprising setting the initial setpoint fuel massbased on engine operating conditions.
 19. The method of claim 15,further comprising injecting a third fuel mass during the first cylindercycle, wherein the third fuel mass is maintained over each of theplurality of subsequent engine cycles.
 20. The method of claim 19,wherein a total mass of fuel injected to the cylinder remains constantover each of the plurality of subsequent cylinder cycles.